Single-particle spectral function of quarter-filled ladder systems

TL;DR

This study investigates the single-particle spectral properties of quarter-filled ladder systems like sodium vanadate using an advanced variational cluster perturbation theory, revealing insights into magnetic phases, band structure, and charge ordering effects.

Contribution

It introduces a generalized variational cluster perturbation theory for extended Hubbard models and applies it to ladder systems, highlighting the role of lattice coupling and inter-ladder interactions.

Findings

Homogeneous antiferromagnetic insulator for small repulsions

Diagonal hopping has minimal effect on bonding bands

Charge ordering influenced significantly by lattice coupling

Abstract

We study the single-particle properties of quarter-filled ladder systems such as sodium vanadate by means of a recently developed generalization of the variational cluster perturbation theory to extended Hubbard models. We find a homogeneous antiferromagnetic insulating phase for nearest-neighbor repulsions smaller than a critical value, without any metallic phase for small repulsions. Different from C-DMFT and LDA considerations, the inclusion of diagonal hopping within a ladder has little effect on the bonding bands, while flattening and shifting the antibonding bands. In the low-temperature charge-ordered phase, the spectrum depends on whether the ordering is driven by the Coulomb repulsion or by the coupling to a static lattice distortion. The small change of the experimentally observed gap upon charge ordering implies that the lattice coupling plays an important role in this ordering. Inter-ladder coupling is straightforward to include within our method. We show that it has only a minor effect on the spectral function. The numerically calculated spectra show good agreement with experimental angle-resolved photo-emission data.